Diaphragm for a loudspeaker

ABSTRACT

A membrane for a loudspeaker is designed so as to facilitate manufacture and to improve the tone of the loudspeaker. The membrane consists of a first plastic film (5a) which serves to retain the shape and a second plastic film (56) laminated to the first film which serves to damper partial oscillations. The membrane is particularly suitable as a conical membrane for a loudspeaker for a television receiver.

BACKGROUND OF THE INVENTION

In a cone loudspeaker, the rearward end of the diaphragm is connectedwith the moving coil and, by way of a centering membrane, with theloudspeaker enclosure while its front end is connected with theloudspeaker enclosure by way of a bead. The centering membrane and thebead cause the diaphragm to be mobile as unimpededly as possible in theaxial direction of the loudspeaker so as to produce the sound pressurebut to be guided in the radial direction of the loudspeaker, i.e. topractically not move at all or as little as possible in this laterdirection. The diaphragm must here be connected with the bead along itsforward circumferential edge.

The tone quality of a loudspeaker is here dependent, inter alia, on theproper functioning of the centering membrane and of the bead, as well ason the behavior of the diaphragm itself.

SUMMARY OF THE INVENTION

It is the object of the invention to configure the diaphragm of aloudspeaker in such a way that, on the one hand, the costs for glueingthe diaphragm to the bead are reduced and the tone quality of theloudspeaker is improved.

The above object is generally achieved according to the presentinvention by a loudspeaker diaphragm which is formed of a two-layermaterial including a first plastic film, for providing formstabilization, having a second plastic film, for damping partialvibrations, applied or laminated to the first film, and with thediaphragm bean for connecting the diaphragm to a loudspeaker enclosurebeing a continuation of the same two-layer material. The modulus ofelasticity of the first and second films is about 2.10³ N/mm² and 10-500N/mm², respectively, and the thickness of the first and second films isabout 200 μm±40 μm and 100 μm±50 μm, respectively.

In the solution according to the invention, the two films which togetherform the diaphragm, each by themselves perform different tasks. Thefirst film, preferably composed of polycarbonate and having a relativelyhigh modulus of elasticity, takes over the task of providing therequired form stability of the diaphragm. It thus gives the diaphragmthe stiffness required for distortion-free reproduction. The second,laminated film is configured as a thermal polyurethane film and servesto dampen partial vibrations of the diaphragm. Compared to the firstfilm, it has a significantly lower modulus of elasticity. With such atwo-layer diaphragm, requirements for form stability of the diaphragm,on the one hand, and damping of partial vibrations, on the other hand,can be met in such a way that the tone quality of the loudspeaker isimproved. The second, thermal film preferably also extends over theouter edge region of the diaphragm and can therefore advantageously beadditionally employed to simplify the process of glueing the bead to thediaphragm. The second, thermal film then serves to dampen partialvibrations in the diaphragm region and additionally for a hot sealingprocess or a hot pressing process in the edge region for fastening thebead to the diaphragm. The diaphragm according to the invention isparticularly suitable for a cone loudspeaker in a television receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of embodiments thereof andreference to the drawing figures wherein in:

FIG. 1 is a schematic sectional view showing the structure of a coneloudspeaker;

FIG. 2 is a partial sectional view of the cone diaphragm FIG. 1 atregion "A"; and

FIG. 3 is a partial sectional view showing another configuration ofdiaphragm and bead at region "B" of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a loudspeaker including an enclosure 1, a magnet 2, amoving coil 3, a centering membrane 4, a conical diaphragm 5 and a bead6. Centering membrane 4 and bead 6 are each connected with the edge ofdiaphragm 5 by means of a hot sealing process, a hot pressing process orby ultrasonic welding. The inner edge of centering membrane 4 isconnected with moving coil 3 and the outer edge of bead 6 with enclosure1.

FIG. 2 shows the structure of diaphragm 5. Diaphragm 5 is a shaped bodycomposed of a first film 5a of relatively great thickness of about 250μm; it is made of polycarbonate and has a modulus of elasticity of about2×10³ N/mm². A second film 5b is vapor-deposited onto the front of film5a, i.e. the surface facing in the direction of sound propagation. Film5b is a thermal polyurethane film having a thickness of about 50 μm anda modulus of elasticity of 10 to 500 N/mm². The second film 5b servesessentially to dampen the partial vibrations of diaphragm 5 in the upperedge region and simultaneously to establish a glue connection betweenbead 6 and diaphragm 5.

The starting material for the diaphragm, i.e. a film as shown in FIG. 2,has a great ability to be curved for a deep drawing process and is thusparticularly suited for cone-type diaphragms.

In FIG. 1 it has been assumed that diaphragm 5 is connected with bead 6.This connection can preferably be effected by a hot glueing process or ahot pressing process while utilizing thermal layer 5b or by ultrasonicwelding. Such a process is disclosed in the older Federal Republic ofGermany patent application P DA-A-3,620,889 published Dec. 23, 1987. Inthe same manner, diaphragm 5 can also be connected with centeringmembrane 4.

FIG. 3 shows another embodiment of the diaphragm and bead 6. In contrastto FIG. 1, diaphragm 5 and bead 6 are composed of the same, continuousmaterial and are produced in one process step by deep drawing from alarge-area material composed of the two films 5a and 5b. For thispurpose, large plates, for example, of a width of about 1.2 m, areproduced by laminating together the two films 5a and 5b. The generallythinner film 5b may also be rolled onto the thicker film 5a. The tonebehavior of the loudspeaker equipped with a diaphragm 5 can beinfluenced as desired by changing the ratio between the thickness D offilm 5a and the thickness d of film 5b. The thickness D of film 5a is,for example, 200 μm±40 μm and the thickness d of film 5b is 100 μm±50μm. In the extreme case, the thickness ratio D/d can thus also lie in anorder of magnitude of 1.

In the deep drawing process, the total thickness (D+d) may be smaller inthe region of bead 6 than in the region of diaphragm 5, with preferablythe thickness ratio D/d being the same for diaphragm 5 and bead 6.

We claim:
 1. A loudspeaker diaphragm comprising: a shaped body oftwo-layer material including a first plastic film for providing formstabilization and a second plastic film applied thereto for dampingpartial vibrations, and a bead which connects an outer edge of thediaphragm shaped body with a loudspeaker enclosure, with said bead beinga continuation of said two-layer material of the diaphragm shaped body,and wherein said first film has a modulus of elasticity of about 2·10³N/mm² and a thickness of about 200 μm±40 μm, and said second film has amodulus of elasticity of about 10 to 500 N/mm² and a thickness of about100 μm±50 μm.
 2. A diaphragm according to claim 1, wherein said firstfilm is composed of polycarbonate.
 3. A diaphragm according to claim 2,wherein said second film is composed of polyurethane.
 4. A diaphragmaccording to claim 1, wherein said second film is composed ofpolyurethane.
 5. A diaphragm according to claim 1, wherein said secondfilm is applied only onto the front surface of the diaphragm which isoriented in the direction of propagation.